t3420: fix under GETTEXT_POISON build

Newly added tests to t3420 in this series prepare expected
human-readable output from "git rebase -i" and then compare the
actual output with it.  As the output from the command is designed
to go through i18n/l10n, we need to use test_i18ncmp to tell
GETTEXT_POISON build that it is OK the output does not match.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t3420-rebase-autostash.sh

@@ -178,7 +178,7 @@ testrebase () {
 		test_when_finished git branch -D rebased-feature-branch &&
 		suffix=${type#\ --} && suffix=${suffix:-am} &&
 		create_expected_success_$suffix &&
-		test_cmp expected actual
+		test_i18ncmp expected actual
 	'
 
 	test_expect_success "rebase$type: dirty index, non-conflicting rebase" '
@@ -275,7 +275,7 @@ testrebase () {
 		test_when_finished git branch -D rebased-feature-branch &&
 		suffix=${type#\ --} && suffix=${suffix:-am} &&
 		create_expected_failure_$suffix &&
-		test_cmp expected actual
+		test_i18ncmp expected actual
 	'
 }